From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f47.google.com ([209.85.160.47]:42616 "EHLO mail-pl0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752167AbeDKHJy (ORCPT ); Wed, 11 Apr 2018 03:09:54 -0400 Received: by mail-pl0-f47.google.com with SMTP id t20-v6so703689ply.9 for ; Wed, 11 Apr 2018 00:09:54 -0700 (PDT) Date: Wed, 11 Apr 2018 00:09:52 -0700 From: Omar Sandoval To: Nikolay Borisov Cc: linux-btrfs@vger.kernel.org, jeffm@suse.com, dsterba@suse.com Subject: Re: [PATCH] btrfs: Fix race condition between delayed refs and blockgroup removal Message-ID: <20180411070952.GA29155@vader> References: <1523430289-29145-1-git-send-email-nborisov@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1523430289-29145-1-git-send-email-nborisov@suse.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Wed, Apr 11, 2018 at 10:04:49AM +0300, Nikolay Borisov wrote: > When the delayed refs for a head are all run, eventually > cleanup_ref_head is called which (in case of deletion) obtains a > reference for the relevant btrfs_space_info struct by querying the bg > for the range. This is problematic because when the last extent of a > bg is deleted a race window emerges between removal of that bg and the > subsequent invocation of cleanup_ref_head. This can result in cache being null > and either a null pointer dereference or assertion failure. > > task: ffff8d04d31ed080 task.stack: ffff9e5dc10cc000 > RIP: 0010:assfail.constprop.78+0x18/0x1a [btrfs] > RSP: 0018:ffff9e5dc10cfbe8 EFLAGS: 00010292 > RAX: 0000000000000044 RBX: 0000000000000000 RCX: 0000000000000000 > RDX: ffff8d04ffc1f868 RSI: ffff8d04ffc178c8 RDI: ffff8d04ffc178c8 > RBP: ffff8d04d29e5ea0 R08: 00000000000001f0 R09: 0000000000000001 > R10: ffff9e5dc0507d58 R11: 0000000000000001 R12: ffff8d04d29e5ea0 > R13: ffff8d04d29e5f08 R14: ffff8d04efe29b40 R15: ffff8d04efe203e0 > FS: 00007fbf58ead500(0000) GS:ffff8d04ffc00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fe6c6975648 CR3: 0000000013b2a000 CR4: 00000000000006f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > __btrfs_run_delayed_refs+0x10e7/0x12c0 [btrfs] > btrfs_run_delayed_refs+0x68/0x250 [btrfs] > btrfs_should_end_transaction+0x42/0x60 [btrfs] > btrfs_truncate_inode_items+0xaac/0xfc0 [btrfs] > btrfs_evict_inode+0x4c6/0x5c0 [btrfs] > evict+0xc6/0x190 > do_unlinkat+0x19c/0x300 > do_syscall_64+0x74/0x140 > entry_SYSCALL_64_after_hwframe+0x3d/0xa2 > RIP: 0033:0x7fbf589c57a7 > > To fix this, introduce a new flag "is_system" to head_ref structs, > which is populated at insertion time. This allows to decouple the > querying for the spaceinfo from querying the possibly deleted bg. > > Fixes: d7eae3403f46 ("Btrfs: rework delayed ref total_bytes_pinned accounting") > Suggested-by: Omar Sandoval > Signed-off-by: Nikolay Borisov > --- > fs/btrfs/delayed-ref.c | 19 ++++++++++++++----- > fs/btrfs/delayed-ref.h | 1 + > fs/btrfs/extent-tree.c | 20 +++++++++++++++----- > 3 files changed, 30 insertions(+), 10 deletions(-) > > diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c > index 5ac2d7909782..20fa7b4c132d 100644 > --- a/fs/btrfs/delayed-ref.c > +++ b/fs/btrfs/delayed-ref.c > @@ -550,8 +550,10 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info, > struct btrfs_delayed_ref_head *head_ref, > struct btrfs_qgroup_extent_record *qrecord, > u64 bytenr, u64 num_bytes, u64 ref_root, u64 reserved, > - int action, int is_data, int *qrecord_inserted_ret, > + int action, int is_data, int is_system, > + int *qrecord_inserted_ret, > int *old_ref_mod, int *new_ref_mod) > + > { > struct btrfs_delayed_ref_head *existing; > struct btrfs_delayed_ref_root *delayed_refs; > @@ -595,6 +597,7 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info, > head_ref->ref_mod = count_mod; > head_ref->must_insert_reserved = must_insert_reserved; > head_ref->is_data = is_data; > + head_ref->is_system = is_system; > head_ref->ref_tree = RB_ROOT; > INIT_LIST_HEAD(&head_ref->ref_add_list); > RB_CLEAR_NODE(&head_ref->href_node); > @@ -782,6 +785,7 @@ int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info, > struct btrfs_delayed_ref_root *delayed_refs; > struct btrfs_qgroup_extent_record *record = NULL; > int qrecord_inserted; > + int is_system = ref_root == BTRFS_CHUNK_TREE_OBJECTID; > > BUG_ON(extent_op && extent_op->is_data); > ref = kmem_cache_alloc(btrfs_delayed_tree_ref_cachep, GFP_NOFS); > @@ -810,8 +814,8 @@ int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info, > */ > head_ref = add_delayed_ref_head(fs_info, trans, head_ref, record, > bytenr, num_bytes, 0, 0, action, 0, > - &qrecord_inserted, old_ref_mod, > - new_ref_mod); > + is_system, &qrecord_inserted, > + old_ref_mod, new_ref_mod); > > add_delayed_tree_ref(fs_info, trans, head_ref, &ref->node, bytenr, > num_bytes, parent, ref_root, level, action); > @@ -878,7 +882,7 @@ int btrfs_add_delayed_data_ref(struct btrfs_fs_info *fs_info, > */ > head_ref = add_delayed_ref_head(fs_info, trans, head_ref, record, > bytenr, num_bytes, ref_root, reserved, > - action, 1, &qrecord_inserted, > + action, 1, 0, &qrecord_inserted, > old_ref_mod, new_ref_mod); > > add_delayed_data_ref(fs_info, trans, head_ref, &ref->node, bytenr, > @@ -908,9 +912,14 @@ int btrfs_add_delayed_extent_op(struct btrfs_fs_info *fs_info, > delayed_refs = &trans->transaction->delayed_refs; > spin_lock(&delayed_refs->lock); > > + /* > + * extent_ops just modify the flags of an extent and they don't result > + * in ref count changes, hence it's safe to pass false/0 for is_system > + * argument > + */ > add_delayed_ref_head(fs_info, trans, head_ref, NULL, bytenr, > num_bytes, 0, 0, BTRFS_UPDATE_DELAYED_HEAD, > - extent_op->is_data, NULL, NULL, NULL); > + extent_op->is_data, 0, NULL, NULL, NULL); > > spin_unlock(&delayed_refs->lock); > return 0; > diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h > index cdf4a94ce5c1..7e7bf4e66d48 100644 > --- a/fs/btrfs/delayed-ref.h > +++ b/fs/btrfs/delayed-ref.h > @@ -139,6 +139,7 @@ struct btrfs_delayed_ref_head { > */ > unsigned int must_insert_reserved:1; > unsigned int is_data:1; > + unsigned int is_system:1; > unsigned int processing:1; > }; > > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index 9a05e5b5089f..ba3468a84f57 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -2616,13 +2616,23 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans, > trace_run_delayed_ref_head(fs_info, head, 0); > > if (head->total_ref_mod < 0) { > - struct btrfs_block_group_cache *cache; > + struct btrfs_space_info *space_info; > > - cache = btrfs_lookup_block_group(fs_info, head->bytenr); > - ASSERT(cache); > - percpu_counter_add(&cache->space_info->total_bytes_pinned, > + if (head->is_data) { > + space_info = __find_space_info(fs_info, > + BTRFS_BLOCK_GROUP_DATA); > + } else { > + if (head->is_system) { > + space_info = __find_space_info(fs_info, > + BTRFS_BLOCK_GROUP_SYSTEM); > + } else { > + space_info = __find_space_info(fs_info, > + BTRFS_BLOCK_GROUP_METADATA); > + } Could you collapse the nested if/else into a big if (head->is_data) else if (head->is_system) else? Were you able to reproduce this on demand? Besides that, Reviewed-by: Omar Sandoval Thanks for fixing this! > + } > + ASSERT(space_info); > + percpu_counter_add(&space_info->total_bytes_pinned, > -head->num_bytes); > - btrfs_put_block_group(cache); > > if (head->is_data) { > spin_lock(&delayed_refs->lock); > -- > 2.7.4 >